A. Inflammatory Bowel Disease
Inflammatory Bowel Disease ("IBD") is the collective term used to describe two chronic, idiopathic inflammatory diseases of the gastrointestinal tract: ulcerative colitis ("UC") and Crohn's disease ("CD"). UC and CD are considered together because of their overlapping clinical, etiologic, and pathogenetic features. From a therapeutic and prognostic standpoint, however, it is important to distinguish them from one another as well as from non-chronic inflammatory diseases of the bowel.
IBD occurs world-wide and is reported to afflict as many as two million people. Onset has been documented at all ages; however, IBD predominately begins in young adulthood. The three most common presenting symptoms of IBD are diarrhea, abdominal pain, and fever. The diarrhea may range from mild to severe and is often accompanied by urgency and frequency. In UC, the diarrhea is usually bloody and may contain mucus and purulent matter as well. Anemia and weight loss are additional common signs of IBD. Reports of an increasing occurrence of psychological problems, including anxiety and depression, are perhaps not surprising secondary effects of what is often a debilitating disease that occurs in people in the prime of life.
B. The Cause(s) of IBD are Unknown
Although the cause(s) of UC and CD is not known, there is general agreement that genetics is important in a person's susceptibility to IBD and that the immune system is responsible for mediating the tissue damage in these diseases. Generally speaking, a failure to down regulate the normal self-limited inflammatory response of the bowel is characteristic of IBD. While a wide range of immunologic abnormalities have been reported in these disorders, none has yet been sufficiently reliable to be of diagnostic value. For example, the production of TNF-.alpha. by macrophages and T cells of IBD patients is a point of controversy. Although it has been suggested that patients with IBD, particularly CD, exhibit elevated TNF-.alpha. protein production and gene expression in the cells of the mucosa, others have not been able to document such a phenomena. Therefore, the diagnostic value of assaying for TNF-.alpha. protein production or gene expression is uncertain. Moreover, a suggestion that this immunologic abnormality has a genetic determinant which would be of value in the diagnosis of CD is necessarily speculative in nature.
C. Methods of Diagnosing IBD
A battery of laboratory, radiological, and endoscopic evaluations are combined to derive a diagnosis of IBD and to assess the extent and severity of the disease. Nevertheless, differentiating UC from CD, as well as other types of inflammatory conditions of the bowel, such as irritable bowel syndrome, infectious diarrhea, rectal bleeding, radiation colitis, and the like, is difficult, because the mucosa of the small and large intestines reacts in a similar way to a large number of different insults. Once infectious-types of bowel disorders have been ruled out, the final diagnosis of IBD is often made on the basis of the progression of the disease. In many patients, though, the diagnosis of IBD must still be regarded as indeterminate because of the overlapping features of UC and CD, particularly with CD of the colon.